Hollow blade anti-crack clamp support blocks

ABSTRACT

An aerodynamic hollow blade clamp support is disclosed. This aerodynamic hollow blade clamp support allows the thin blade wall to resist deformation and cracking from blade clamp pressure stress. These hollow blade clamp supports fill the blade hollows for at least the blade length under the blade clamps. These hollow blade clamp supports reduce the number of integral blade support webs and thus the weight of the overall blade length. The reduction of hollow blade weight reduces blade centrifugal stresses during blade rotor overspeed.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was first disclosed in an unsuccessful federal research grant application dated Mar. 16, 2005. The Dept. of Energy financial opportunity number is DE-PS3605GO95012.

STATEMENT REGARDING A JOINT RESEARCH AGREEMENT

Not Applicable

REFERENCE TO A SEQUENCE LISTING

Not Applicable

CROSS REFERENCE OF RELATED APPLICATIONS

60/783,475

BACKGROUND

1. Field of the Invention

This invention relates to vertical axis wind turbines, which are used to convert wind energy.

2. Description of the Related Art

The Darrieus-type vertical axis wind turbine, (VAWT) having its rotating shaft traverse to the air stream, was patented by G. M. Darrieus in the United States in 1931 U.S. Pat. No. 1,835,018. The Darrieus-type vertical axis wind turbine is said to resemble an egg-beater with curved blades connected at both ends to the ends of the rotating shaft.

Each blade of the turbine is symmetrical in cross section and is curved in the shape of a perfectly flexible cable of uniform density and cross section would assume if spun about a vertical axis. This curved blade shape is represented by the Greek word “troposkein” meaning turning rope. With VAWT blades having a troposkein shape, major stresses are in tension when the rotor is spinning. Thus, rotation of the turbine rotor will not cause the blades to bend significantly nor to produce significant blade bending stresses.

The operational principal of the vertical axis wind turbine (VAWT) is analogous to the aerodynamics of a wing (airfoil) as is described in “The Wind Power Book” pages 78 and 79 by Jack Park. Fluid forces on the blades of the VAWT are divided into lift and drag forces. A component of the lift force causes rotor rotation and a component of the drag force opposes rotor rotation. The rotor torque will be positive as long as the driving component of the lift force exceeds the opposing component of the drag force. With such a rotor the aerodynamic efficiency is low or negative at rotor tip speed over wind speed ratios below 2 or above 9. Consequently, a motor must usually be employed to start the turbine.

Interest in the Darrieus-type vertical axis wind turbines has been stimulated in recent years by the energy crisis and the important advantages of such turbines over horizontal axis machines which include the following: (1) The VAWT accepts wind from all directions and therefore does not require costly direction orientating equipment. (2) The VAWT does not require adjustment of blade pitch to limit maximum power output at high wind speeds. (3) The generator, speed reducer and brake do not have to be supported as part of the wind orientating platform. (4) The VAWT blades are supported at both ends which makes for less expensive and longer lasting blades.

VAWT designs have advanced and have inherent advantages over horizontal axis machines. But a VAWT is needed to be more cost effective in construction, erection, maintenance and operation.

Inventors have made attempts to create a VAWT that will prosper with the stable energy price following the panic of 1973.

U.S. Pat. No. 6,364,609 to Barnes discloses a VAWT having an erection gin pole with a combination hold down and stabilizing gin pole that allow pivot erection using a ground mounted winch. These gin poles provide tension reduction for the erection and hold down cables that hold the turbine together during pivot erection.

This disclosure also describes a curved blade end mounting arrangement with elongated bolt holes cut through these blade ends. These elongated bolt holes unnecessarily weaken the blade ends.

SANDIA LABORATORIES report SAND-84-1287 FIGS. 8 and 11 show a VAWT blade end mounting clamp.

SANDIA LABORATORIES report SAND-84-1287 FIG. 10 shows details of the hollow blade end to be clamped. SAND-84-1287 FIG. 10 shows a 1.22 meter chord length NACA 0021 blade end. The FIG. 10 blade end faces are perpendicular to the blade skin. The FIG. 10 blade is composed of three aluminum extrusions bolted together. The chord line in FIG. 10 extends from the outermost edge of the blade nose to the outermost edge of the blade tail. The chord line in FIG. 10 appears as a straight center line because the curve of the blade skin above the chord line is the mirror image of the curve of the blade skin below the chord line. Note also the FIG. 10 blade has eleven skin support webs.

Report SAND-84-1287 FIG. 10 support webs run into the page and therefore the length to the blade. These FIG. 10 support webs add to the overall weight of the blade. The center lines of the blade support webs are perpendicular to the chord line. The FIG. 10 blade skin support webs prevent the skin from cracking under blade clamp pressure.

A blade skin clamp support is needed to support the skin only for the blade length under the clamp. This hollow blade clamp support is needed to reduce the number of blade skin support webs. Reducing the number of hollow blade support webs, reduces the weight per foot of the blade. This blade weight reduction per foot reduces the cost of the blade, since aluminum extrusions are sold on a dollars per pound basis. Blade weight reduction also reduces centrifugal stresses for potential rotor overspeed and reduces rotor tower weight to withstand centrifugal stresses from rotor overspeed.

BRIEF SUMMARY OF THE INVENTION

In accordance with the present invention, a hollow blade is disclosed. This blade has two hollow openings separated by one integral center web. These two blade openings have each a close fitting solid bar stock support block.

BRIEF DESCRIPTION OF THE DRAWING VIEW

PAGE 1/1: A plan end view of a wind turbine blade and wind turbine blade clamp.

DETAILED DESCRIPTION OF THE INVENTION

A typical embodiment of the hollow blade, the blade anti-crack support blocks and the blade clamp of the present invention is shown in the drawing (end view). Reference numeral 1 (with the arrow) designates the entire blade end and blade end clamp assembly. All blade clamp end view surfaces except, for the blade 2 end surface, are shown with hatch lines. The blade clamp end surface hatch lines make it easier to see the thin wall of hollow turbine rotor blade 2. Reference numeral 1 represents all reference numerals except numeral 8.

The end view of hollow blade 2 is shown in the drawing without hatch lines in the blade wall and integral wall support web 5. Blade 2 is a thin wall metal form with two hollows separated by integral wall support web 5. This hollow metal form extends uniformly into the drawing page. This hollow blade 2 is best made as a hot metal alloy extrusion. This hollow blade 2 can also be made as a hot plastic extrusion. Hollow blade 2 has an aerodynamic teardrop shape where the tail is the narrower end. The blade 2 shape is also described as a modified ellipse. The nose of blade 2 has a larger radius than the blade tail. The blade 2 straight chord line can be imagined as extending from the nose edge farthest from the support web 5 to the tail edge farthest from both the blade nose and support web 5. The blade 2 imaginary chord line is straight because blade 2 wall has the same curvature above the chord line as below the imaginary chord line. Blade 2 is described as symmetrical about the imaginary chord line.

The blade nose support block 4 is shown with hatch lines that are oblique to the blade 2 imaginary chord line. This blade nose support block 4 has a close tolerance fit with the blade nose hollow between support web 5 and the nose wall inside surface. Blade nose support block 4 is best made as a hot metal alloy extrusion. Blade nose support block 4 can also be made as a hot plastic extrusion. The nose support block 4 extends into the blade nose hollow for at least the length of the blade clamp plates 6 and 7. The blade nose support block minimizes buckling of the blade nose wall and therefore cracking of the blade nose wall, under clamp pressure from blade clamp plates 6 and 7.

The blade tail support block 3 is shown with hatch lines that make a different angle with the blade imaginary chord line than block 4 hatch lines. Blade tail support block 3 makes a close tolerance fit with the blade tail hollow between blade support web 5 and the blade tail wall inside surface. Blade tail support block 3 is best made as a hot metal alloy extrusion. Tail support block 3 can also be made as a hot plastic extrusion. The tail support block 3 extends into the blade tail hollow for at least the length of the blade clamp plates 6 and 7. The tail support block 3 minimizes the buckling of the blade tail wall and therefore tail wall cracking under the clamp pressure from blade clamp plates 6 and 7.

Blade support blocks 3 and 4 may extend into blade 2 beyond the length of plates 6 and 7 to add strength and stiffness to blade 2.

Clamp plate 6 is the outer clamp plate farthest from hub plate 8. Clamp plate 6 has hatch lines shown on the end edge in the drawing view. Clamp plate 6 also includes two rectangular end section bolt flanges nose clamp bolt flange 19 and tail clamp bolt flange 21. Clamp plate 6 with clamp bolt flanges 19 and 21 extend into the drawing page. The center section of clamp plate 6 between clamp bolt flanges 19 and 21, has a surface that closely fits and contacts the outer curve of the blade 2 wall. This plate 6 contact curve is incomplete and does not contact the outermost nose and tail surfaces of blade 2. Clamp plate 6 is best formed as a hot metal alloy extrusion.

Hub clamp plate 7 has four integral rectangular end section flanges, nose clamp bolt flange 20, tail clamp bolt flange 22 and blade hub mounting flanges 15 and 16. Clamp plate 7 with integral flanges 15, 16, 20, and 22 extends into the drawing page. The drawing view shows the end edge of plate 7 with hatch lines. The center section of hub clamp plate 7, between clamp bolt flanges 20 and 22, has a surface, opposite to hub bolt flanges 15 and 16, that closely fits and contacts the outer curve of the blade 2 wall. This clamp plate 7 contact curve is incomplete and does not touch the outermost nose and tail ends of the teardrop shaped blade 2.

The incomplete contact curves of both clamp plates 6 and 7 provides a gap between plates 6 and 7 near both the nose and tail of blade 2. These blade nose and tail gaps between clamp plates 6 and 7, allow for consistent clamp pressure to be applied to blade 2 by the contact curves of both clamp plates 6 and 7.

Hub plate mounting bolt 17 passes through aligning hub mounting holes in hub mounting flanges 15, 16 and hub plate 8. Mounting bolt 17 connects mounting flanges 15 and 16 to hub plate 8. Hub plate mounting nut 18 is threaded to bolt 17 to hold bolt 17 in the aligning hub mounting holes. Several of these aligning hub mounting hole sets and hub mounting bolts extend into the drawing page along the length of flanges 15, 16 and hub plate 8. These additional hub mounting bolts identical to bolt 17 are blocked from view in this end plan view drawing by bolt 17 and nut 18. Additional hub plate mounting nuts are threaded to the additional hub plate mounting bolts and are blocked from view by identical mounting nut 18. Hub clamp plate 7 is best formed as a hot metal alloy extrusion.

Blade nose clamp bolt 9 is mounted through aligning holes in nose clamp flanges 19 and 20. Nose clamp nut 10 is threaded to bolt 9 to hold together nose flanges 19 and 20. Nose clamp bolt washers 11 are aligned and mounted on bolt 9 to better distribute clamping stress across flanges 19 and 20. Blade tail clamp bolt 12 is mounted through aligning holes in tail clamp flanges 21 and 22. Tail clamp nut 13 is threaded to bolt 12 to hold together tail flanges 21 and 22. Tail clamp bolt washers 14 are aligned and mounted on bolt 12 to better distribute clamping stress across flanges 21 and 22. Clamp pressure on blade 2 between clamp plates 6 and 7 is best obtained, by alternately threading nuts 10 and 13 one half turn at a time.

Additional blade clamp bolts identical to bolt 9 are similarly mounted as bolt 9 to clamp bolt flanges 19 and 20, as these flanges extend into the drawing page. Additional clamp nuts identical to clamp nut 10 are similarly mounted as nut 10 to clamp bolt flanges 19 and 20, as these flanges extend into the drawing page. These additional blade nose clamp bolts and nuts are blocked from view in the drawing by bolt 9 and nut 10. Additional tail clamp bolts and nuts are similarly mounted to clamp flanges 21 and 22 as bolt 12 and nut 13. These additional mounted tail clamp bolts and nuts are blocked from view in the drawing by bolt 12 and nut 13.

The drawing shows how a lightweight thin wall, hollow, aerodynamic blade 2 can be securely clamped to a wind turbine rotor without damaging the blade 2 wall through the use of close fitting hollow blade support blocks 3 and 4. The drawing also helps visualize how hollow blade support web 5 can hold the hollow blade 2 teardrop cross section shape when the blade length is permanently bent to approximate a vertical axis wind turbine rotor troposkein curve.

Although a preferred embodiment of the invention has been selected for illustration and description, it will be apparent that numerous modifications can be made therein without departing from the invention or the scope of the claims attached hereto.

Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given. 

1. A blade end clamp assembly comprising: an aerodynamic hollow blade, said hollow blade comprising a thin wall with a nose hollow and a tail hollow separated by an integral wall support web. two blade clamp plates that apply clamp pressure to said aerodynamic hollow blade, a blade nose support block that closely fits inside said blade nose hollow to minimize said blade nose wall buckling and cracking, a blade tail support block that closely fits inside said blade tail hollow to minimize said blade tail wall buckling and cracking. 